HK1145943B - Filtration of vegetable slurries - Google Patents

Abstract

Discloses a two stage filtration system for treatment of fibrous vegetable matter, particularly oilseed materials such as oil-extracted canola flakes to separate the low valued fibrous material from soluble material and small non-structural water-insoluble material of higher value. The filtration system receives a vegetable matter slurry and passes the slurry through first stage filter which is an impeller type filter that operates to separate the slurry into a filtrate and a moist retentate. The moist retentate is further filtered in a second compression filtration stage or a centrifuge to remove additional water. Small non-structural insoluble matter is removed in the filtrate.

Description

Filtration of plant pulp

The application is a divisional application of Chinese patent application for filtration of plant pulp (application No. 200380107959.5, application date: 24/11/2003).

Technical Field

The present invention relates to the extraction of carbohydrates and/or proteins from crushed or treated plant matter, and is particularly useful for recovering valuable proteins and carbohydrates from oil seeds from which oil has been extracted.

Background

Plants often contain valuable materials such as proteins and valuable non-structural carbohydrates that are mixed with low value fibrous materials such as skins and plants. Some valuable proteins and carbohydrates are generally water soluble, but not all proteins and carbohydrates are soluble in water. Many water insoluble valuable proteins and non-structural carbohydrates are shown as smaller particulate matter than fiber.

A particular group of products containing quantities of carbohydrates and proteins are oilseed materials from which oil has been extracted. These materials also include a significant amount of residual oil in the case where the oil has been removed by degreasing using a cold pressing method. In degreasing by solvent methods, a small amount of oil is present. In particular, the product remaining after oil extraction with rapeseed is a resource rich in valuable proteins and carbohydrates, and is called defatted rapeseed flakes. Such oilseed materials also contain low value fibrous materials such as peels and stalks which should be removed in order to obtain a higher value product.

One method of separating low value fibrous material from water soluble high value material is by aqueous extraction. In aqueous extraction, water is added to the plant material to form a thick slurry. Typically such slurries consist of three distinct phases: a liquid phase comprising water soluble components of the feedstock; a light particulate phase consisting of suspended particulate matter; a heavy solid phase consisting of fibrous material such as bark and residual stalks. Extraction processes are typically designed to remove only the liquid phase from the slurry. This method uses known separation techniques such as centrifugation, which is designed to produce a clear liquid extract. However, the suspended fine particulates, which contain valuable proteins and carbohydrates, are transferred to the solid residue in any separation system that produces a clear extract. Therefore, chemical modification is often applied to increase the solubility of the protein in the slurry. However, this modification increases the cost of the process and may compromise the nutritional value of the extract.

It would be advantageous to provide a mechanical separation system that is capable of directly separating fine particulates into an extraction liquid, thereby producing an extraction liquid that includes both a liquid phase and a light particulate phase containing valuable fine particulates. This allows recovery of soluble and insoluble (small particulate) non-fibrous non-structural materials. Such insoluble small particulate matter is often rich in valuable materials such as carbohydrates and proteins.

However, when many of the broken plant products are slurried, the liquid portion of the slurry is very thick and viscous. This is because of the presence of various water soluble or partially water soluble proteins and carbohydrates that enter the aqueous phase of the slurry. In defatted canola, some residual oil is also present. In addition, after the defatting process (especially in the case of making defatted canola flakes), there may be some small particles of cell meat. These particles are rich in proteins and are therefore particularly valuable for recovery.

In the case of a thick and viscous starting slurry of vegetable material, such as an oil-extracted rapeseed flake slurry, it is quite difficult to obtain an effective extraction rate of the liquid phase and the light plasmid phase. Pressure based filtration methods may be employed to obtain an extraction liquid comprising a light particulate phase. In this process, the slurry is pressurized with a filter medium having micropore openings or pores which allow the passage of the light particulate phase of the slurry to the heavy particulate phase, thereby turning the heavy particulate into an extracted cake. Examples of this type of process are shown in PCT published patent applications WO 01/87083 and WO03/047438 to Maenz et al. However, the thick and sticky nature of the slurry causes the filter media to be compacted, the separation per unit area of the filter media is poor, and the slurry is significantly squeezed out from both sides of the filter media. Therefore, direct treatment of viscous slurries of vegetable material by pressure filtration as in the PCT published application requires a large filtration area and slow filtration rates. Therefore, a large apparatus is required, which increases the production cost.

U.S. patent 5814230 to Willis et al discloses a method and apparatus for separating coarse and ultrafine particles from a liquid stream. In this method, a plurality of filter screens having various pore sizes are continuously passed through the particulate matter containing aerosol until a filter cake is formed on the surface of the filter screen and a clear, particulate-free liquid phase is obtained. These particles are then removed from the screen and dewatered by methods such as vibration and direct air blowing, or by pressure dewatering. The plurality of filter screens with gradually smaller pores are designed to produce a clear filtrate free of particles, so that in the case of extraction of a plant slurry, valuable debris-like powder of cell meat is not present in the filtrate formed by this method.

Glarer, U.S. patent 4975183, teaches automatically raising and lowering the agitation device during pressure filtration of a slurry containing particulate matter to produce a more uniform filter cake on the filtration surface thereby enhancing the operability of the filtration process. This method is said to be capable of improving the conventional single-stage pressure filtration method.

U.S. patent 4921615 to Lindoerfer et al describes a multi-stage pressurized process for removing particulate matter from a viscous liquid. In this process, a viscous feed slurry containing particulate matter is pressure filtered in a series of process steps involving a filter material having a gradually decreasing pore size. This process is designed to produce a clear liquid filtrate.

Impeller-driven filtration methods are known. In this filtration method, rotating impeller blades rotate adjacent to the filter media as the slurry passes over the same filter media. The action of the impeller repeatedly sweeps the slurry over the filter media, minimizing the solidity of the slurry on the filter media. However, impeller-driven filtration tends to leave a residue rich in moisture.

Centrifugation is a known filtration method. However, centrifugation is not effective for viscous plant slurries because the viscosity of the slurry does not allow the desired separation using existing centrifugal filtration methods.

Thus, the well-known separation apparatus and method do not provide a practical and useful means for separating water-soluble protein and small cell meat particles (when present) from the remainder of the plant material, particularly for viscous slurries. In addition, these devices and methods may leave a residue with significant moisture, and therefore require a large amount of energy to dry.

Disclosure of Invention

The present invention describes a two-stage high capacity filtration system suitable for separating viscous feed slurries. The effect of the present invention is to effectively separate the viscous aqueous extract containing water soluble components and valuable small particulate cell meat (if present) from the rest of the plant material. The final residue resulting from the process of the invention can then be dried without consuming large amounts of energy. The invention is particularly useful for separating useful carbohydrates and proteins from defatted oilseeds, particularly defatted canola flakes.

In the filtration system of the present invention, the first stage filtration is performed by an impeller-driven filtration method, and then the second stage filtration is performed by a pressure filtration method or a centrifugal separation method.

Drawings

The invention is described in connection with the following figures, wherein:

FIG. 1 shows a first embodiment of a filter device of the present invention;

FIG. 1a is a partial cross-sectional view showing a modification of the embodiment of FIG. 1 using a helical compression device;

FIG. 2 shows a second embodiment of the filter device of the present invention;

fig. 3 shows a third embodiment of the filter device according to the invention.

Detailed Description

In the present invention, the first stage filtration is carried out by impeller-driven filtration. The pore size ("micropore aperture") of the filter media may be such that suspended fine particulates can pass through the micropores while large particle size particulates, larger than the largest pore size of the filter, remain on the filter media to form a residue. The sweeping action of the impeller is then used to scrape the residue from the surface of the filter media, thereby removing it from the area being filtered.

In filtering defatted oilseed slurries, particularly defatted oilseed rape, the perforations are preferably selected so that they pass only through fine particles, leaving behind undesirably large plant particles. The residue from the drive impeller filtration still contains a significant amount of moisture. This residue cannot be dried conveniently and is costly to dry. Therefore, a second stage of filtration is employed. The second stage filtration may be centrifugal filtration or pressure filtration.

Centrifugal filtration is not optimal because of the large volume of the residue. This means that a large centrifuge is required, which increases the cost of operating the apparatus. In addition, the moisture of the solid phase residue remaining after centrifugation is generally higher than that obtained by compression filtration. However, as the second stage filtration, centrifugal filtration may be employed because the viscous fluid in the raw slurry becomes less viscous after passing through the impeller filter.

The pressure filtration gradually reduces the volume of the material to be filtered. There are several kinds of pressure filtration.

In a pressurized filtration, a piston may be used to pressurize the residual material to be filtered against the filter media, thereby squeezing out the remaining liquid.

Another type of pressure filtration involves a continuous process in which a moisture-laden feed material is continuously fed to the inlet section of the apparatus, then the feed material is passed under pressure through a press whereby moisture is forced out of the filtration surface, and then the dewatered cake is discharged at an outlet section. Two examples of continuous pressure filtration systems are the use of belt or screw presses. The filter pressurized by a belt press or a screw press has the advantage that it can be processed continuously, whereas piston pressing can only be processed batchwise.

If desired, the liquid from the remainder of the pressurized and centrifugal filters may be mixed with the liquid from the impeller-driven filtration stage. Alternatively, to reduce the overall water consumption, the filtrate of the residue can be used as the input water for the impeller filter and the impeller filter filtrate can be discharged as the final liquid product. In addition, if desired, the smallest pores of the filter medium during piston pressurization, or the belt press-selected perforated holes, may be of such a size that the holes can pass through flakes of cell meat entrained in the residue, which flakes can be leached out with the liquid being pressed out.

The smallest aperture of the filter medium can be selected according to the largest size solid particulate matter that is desired to pass through the filter. This choice preferably takes into account the general particle size of the cell meat particles or the particle size of other valuable small particulate matter present. In the case of defatted canola, the maximum particle size of the cell meat particles is typically as large as about 75 microns. Accordingly, the filter media preferably has a minimum pore size of at least 100 microns, and most preferably a minimum pore size of 150 microns. In order to allow the cell meat to enter the filtrate. The maximum perforation is not critical as long as it is small enough not to penetrate the fibrous material present. Filter media with a maximum pore size of up to 2500 microns can generally be used because most fibrous materials such as skins or stems (which are required to remain in the retentate after filtration) generally cannot pass through filter media of this size. However, in the presence of smaller flakes of skin and stem, the maximum pore size can be reduced accordingly, particularly because there are few cell meats whose maximum diameter exceeds 75 microns. Therefore, it is generally preferable that the maximum pore is 190 μm or 250. mu.m.

By "maximum aperture" and "minimum aperture" of the filter media is meant the average maximum or minimum size (as the case may be) of the filter media pores. If the holes are substantially circular and of uniform size, the largest and smallest holes are the same, both referring to the diameter of the hole (sometimes referred to as the "micropore size"). If the apertures are approximately square in cross-section, the largest aperture is the diagonal of the square and the smallest aperture is the side length. Generally, rather than having apertures with one dimension (e.g., length) much greater than the other dimension (e.g., width), it is preferred to have round or square apertures, or rectangular apertures with side and end edges of little difference in length. Therefore, the largest and smallest pores are preferably not very different from each other. The pores should also have approximately the same cross-section throughout the thickness of the filter media to prevent particulate matter from becoming lodged on the filter media. Most impeller filter or belt filter media are wire or fabric meshes, between alternating parallel wires or wires. Having uniform square or nearly square holes in the case of a belt press, if one wants to pass small particles (e.g., cell meats) through the belt, it is considered that the thickness of the belt and the weave structure of the material, in addition to the size of the holes, also affect the passage of the particulate matter through the belt.

Several embodiments of the present invention are described below with reference to the accompanying drawings.

Fig. 1 illustrates a preferred embodiment of the present invention, and in fig. 1, a slurry forming stage, generally designated by the numeral 10, is shown. Defatted oilseeds 1 (or other plant products containing soluble protein and/or carbohydrate in a predominantly fibrous solid and small particles of insoluble protein and/or carbohydrate) and water 2 are placed in a vessel 12. In this vessel 12, they are mixed and stirred by an impeller 13 to form a slurry 100. The slurry 100 is then periodically discharged from the vessel 12. This operation can be performed in a convenient way, and in the exemplary embodiment shown, is performed using a discharge pipe 15. The discharge pipe is fitted with a suitable valve 14 to close the pipe until the defatted oilseed 1 and water 2 have been mixed to form a slurry 100 of the desired homogeneity.

Slurry 100 discharged through pipe 15 enters an impeller driven filter generally indicated by the numeral 20. The impeller-driven filter has a filter medium 21, which is preferably a mesh formed into a tube. The mesh surrounds an impeller 22 which is an auger that abuts the mesh 21 forming the tube. The slurry 100 passes through the meshed pipe 21 and the auger. As the auger pushes the slurry up and forward, the auger sweeps away the slurry from the filter medium 21 because the auger is in close contact with the mesh filter medium 21. The mesh has a sufficiently large mesh size (the smallest pores) so that the small pieces of cell meat in the slurry can pass through the mesh and enter the container 23 along with the liquid. Thus, the liquid contains the fluid 101 filtered out of the slurry and the cell meat particles 102 that also pass through the mesh 22. The liquid 101 and the cell meat particles 102 together are rich in protein and, after further processing, can result in a very valuable food or animal feed, or food additive.

Exiting the top of the auger is an aqueous residue 103 that remains after the liquid 101 and cell meats 102 have been filtered from the slurry. The residue is passed to a pressure filter in the form of a belt press 30. The figure shows schematically a belt press 30 having an endless belt 31 and an endless belt 32, the endless belt 31 rolling on rollers 33 and the endless belt 32 rolling on rollers 34. The belts are oriented so that they roll in a serpentine path over the rollers so that the material between the belts is under increasing pressure as the mixture moves from the left to the right in fig. 1. As the belts approach each other, liquid is squeezed from the residue 103 and falls, forming a liquid 104 in the container 35. At outlet 36 the residue has been substantially dewatered and extruded out of outlet 306 as a substantially solid press cake 105 which is then cut or shredded by knife 40 and falls as product 106 into bucket 41. The product is suitable for use as feed for ruminants.

FIG. 1a is a cross-sectional view of another form of a pressurized filter that may be used in the system shown in FIG. 1. The residue 103 enters a pressure filter in the form of a screw press 70. A cross-section of the screw press 70 taken through the housing is shown. The manner of operation of this form of screw press is thus illustrated. The archimedes screw 72 rotates in the housing 71 and pushes the residue 103 entering from the right, along the channel formed by the housing 71, to the right in the figure. The archimedes screw pump has a non-threaded portion 77 that gradually increases in diameter from the left side to the right side of fig. 1 a. The cross-section of the channel formed by the casing 71 and the spiral 78 therefore decreases from left to right. As the screw rotates, the reduction in cross-sectional area through the channel material increases the pressure on the material, causing liquid to be expressed from the screw press through the filter media 73 disposed along the internal length of the screw press. The liquid flows out along a channel 75 through which the liquid can flow to the container 35 shown in fig. 1. At the end of the filter, the residue 103 has been compressed and extruded from the filter through the channel 76 as a press cake which is then introduced into the barrel 41 shown in fig. 1.

Fig. 2 shows a modification of fig. 1. In fig. 2, the same reference numerals as those in fig. 1 denote the same parts. The embodiment of fig. 2 does not use a belt press 30 but a piston press 50. The piston press 50 has a compression chamber 51, one end of which is formed by a mesh 52. The compression chamber 51 is suitably cylindrical but may be of other shapes if desired, provided that it is capable of cooperating with a piston to compress the residue 103 therein. The residue 130 with moisture is fed into the compression chamber 51 (e.g., by conveyor 20) where it is placed on the end 52 of the web. When the cylinder is filled with a discrete portion of the aqueous residue, the delivery of the residue 130A is stopped. This stopping can be accomplished by using the conveyor belt 29 to transfer it to a storage container (not shown) or by closing the auger 22 so that no material is placed on the conveyor belt 29.

The piston 53 is then lowered into the compression chamber 51, compressing and squeezing the residue 103, thereby pressing out the liquid 104, which is collected in the reservoir 35. The piston is then withdrawn and the residue is removed as a pressed cake 105A. The pressed cake may be conveyed by a suitable conveyor belt 42 to a cutter 40 where the residue is cut into a sheet-like powder which falls into a bucket 41 to form a product 106A. The product 106A resulting from this embodiment is substantially the same as the product 106 resulting from the first embodiment described above, except that the product 106A resulting from this embodiment is somewhat drier than the product 106 resulting from the first embodiment, depending on the pressure exerted by the piston 53 in the compression chamber 51 and the time difference of pressurization. Drying the product is of course an advantage, since only a slight drying is then necessary. This cannot therefore be compensated for the fact that the process shown in fig. 2 is discontinuous, rather than the continuous process shown in fig. 1. In general, the process shown in FIG. 1 requires less labor to fill the compression chamber and then insert the piston into the compression chamber than the process shown in FIG. 2.

Fig. 3 shows a third embodiment of the invention. In showing the same components, the same numbering is used in fig. 3 as in fig. 1 and 2.

The embodiment of fig. 3 shows a different type of impeller filter than that of fig. 1. In fig. 3, the impeller filter is an open vessel, generally designated 60, having a sidewall 61 and a mesh bottom 62. The vessel has therein a paddle-shaped impeller, generally indicated at 63, having paddles 64 rotating about a power shaft 65 axis. As the paddle 64 rotates, it pushes the slurry against the screen 62. In this way, the liquid 101 with the cell meat 102 therein can be pressed into the container 23 below.

The transport of defatted rapeseed 1 and water 2 was stopped from time to time. The paddles 64 are constantly operated until substantially no more liquid passes through the mesh 62. What remains in the container 104 is a residue 103B, which is different from the residue 103 of the first embodiment or the residue 103A of the second embodiment. The impeller 63 is then removed and the residue in the vessel 60 is decanted off, placed on the conveyor belt 29 and conveyed to the second stage. The residue is a residue 103B with moisture.

In the embodiment shown in fig. 3, the second stage filter is a batch filter centrifuge, generally designated 80. The centrifuge has a central shaft 81 driven by a motor 82. The shaft supports an arm 83 having a separation vessel (shown in phantom) mounted at the end. The separation vessel is shown at 84 in one position and at 84A (in dashed lines) in a second position. A hinged device (not shown) may access the separation vessel. In operation, the separation vessel (initially in the position indicated by dashed line 84A) is charged with aqueous residue 103B, as schematically indicated by arrow 91. The centrifuge is operated to separate the liquid from the residue. The centrifuge rotation is then stopped with the separation vessel at position 84 indicated by the solid line. The residue 103B with moisture is thus separated into a solid 105B (which is substantially similar to the solid press cake 105) and a liquid 104. Liquid 104 and solids 105B are then removed from the centrifuge as indicated by arrows 95 and 96, respectively. The solid 105B may be cut with the cutter 40 into flakes 106B similar to the flakes 106 or 106A of the product in the previous embodiment.

A continuous centrifuge may be used instead of the batch centrifuge shown.

In each of the above embodiments, the liquid 104 is rich in protein and can be used directly as food or animal feed, or mixed with the liquid 101 (and entrained cell meat 102) and used directly as food or animal feed. Alternatively, to reduce the water demand of the process, the liquid 103 may be used as the liquid delivered to the first stage without water 2, or mixed with some water 2 as a supplement, as shown by the short-line arrows 110 and 111, respectively. If the liquid 104 is circulated in this manner, the liquid product may be continuously or intermittently withdrawn from the container 23, as indicated by arrow 112.

In many cases, it is desirable to reuse one or more of the filtration stages in order to enhance the recovery of protein from the liquid product. Thus, it is sometimes desirable to re-mix the product 106, 106A or 106B with water to form a slurry and re-perform the first and second stages of filtration. Thus, this process can be repeated a second time (or more than two times) with the product 106, 106A or 106B as input for the first stage without using oilseed 1. This filters out other water soluble proteins and smaller particles of cell meats, allowing more of the valuable proteins and carbohydrates of the defatted oilseed or other vegetable product to be recovered in the liquid products 101 and 104.

In some cases, it is also necessary to recycle the aqueous residue 103, 103A or 103B to the vessel 61 for one or more first stage filtrations to be repeated before the aqueous residue is transferred to the second stage by the conveyor belt 29. This operation is schematically shown in the figure by a dashed line. The second stage filtration unit (pressurized filter or centrifuge) is more costly than the first stage filtration unit. Thus, repeating the first stage of filtration allows more protein product to be filtered into the vessel 23, thereby requiring fewer operations of the second stage while still maintaining good extraction efficiency.

The ratio of water to defatted oilseed or other vegetable material used in this process can vary significantly. High water ratios (more water used) generally improve extraction efficiency. However, the equipment costs are higher because the equipment required to handle large volumes of water and liquid streams is large in scale. Low moisture ratios result in an overly concentrated slurry that is difficult to transport and does not adequately extract valuable protein. In general, for rapeseed flakes, a water/oilseed ratio of about 2.5: 1 to 2.0: 1 (by weight) is preferred. And preferably the water is also heated, for example to 50-75 c (to help dissolve proteins and carbohydrates in the water). However, the ratio of water to plant product and the water temperature depend primarily on the processing benefits of the particular device and do not limit the disclosed process.

The impeller filter 60 shown in fig. 3 can be used in the embodiments shown in fig. 1 or fig. 2 instead of the impeller filter 2 shown in these figures. Centrifuge 80 (or a continuous centrifuge) may be used in the embodiments shown in fig. 1 or fig. 2 in place of the pressurized filter used in these embodiments. Importantly, impeller stage filtration is to remove large amounts of viscous liquid, followed by a second stage of pressure filtration or centrifugal filtration to reduce moisture.

The present invention is further illustrated below by means of comparative examples.

Example 1

(comparative example, only belt press was used).

In this example, rapeseed flakes were mixed with water and filtered only with a pressure filter (this device is indicated by the reference numeral 30 in fig. 1). The product 106 is then suspended from it in a small amount of water and filtered again using a belt press.

15kg of oil-pressed desolventized rapeseed flakes were mixed with 90kg of water at 60 ℃ to form a slurry (6 parts of water: 1 part of raw material flakes), mixed for 10 minutes or more, and mixed until uniform. Thus a very viscous slurry was obtained. The slurry was fed to a 7-roll sub-belt filter press (model EJ-25-9 press from Frontier Technologies, Allegan, michigan, usa) equipped with a 2 x 12 inch belt (350 inch 3/min air passage holes). (such means is shown schematically at 30 in figure 1). The slurry is compressed between the belts, thereby separating the filtrate containing small particles of cell meat from the filtered residue. The belt pressure was maintained at a constant 80 psi. The processing speed can be adjusted to a maximum according to the amount of slurry entering the press without being extruded from the side edges of the belt, while maintaining the allowable final pressed cake dry matter of greater than 30%. The belt treatment speed was calculated as the amount of dry white flake powder in the slurry treated per meter of belt width in minutes. The weight and dry matter content of the filtrate and the first press cake were determined.

The first filtered cake was again mixed with 60kg of water at 60 ℃ to form a slurry so that the total amount of water used in the second filtration was equal to 10 times the water to 1 part of the dried canola flake powder. The second slurry has a lower viscosity than the first slurry, but still has a significant viscosity. The slurry was then processed using a belt filter press as described above. The filtration rate and measurements of the filtrate and cake were as described for the first filtration.

The twice filtered filtrates (102 and 104) were mixed and the total weight, dry matter content and filtration efficiency were measured. The suspended particles were determined as the percentage of particles deposited on the bottom of the centrifuge tube to the total volume of filtrate after 5 minutes of centrifugation at 5000 r/m.

Example 2

(example of the invention is used).

In this example, the apparatus schematically shown in FIG. 1 (impeller filter schematically shown at 20, followed by belt press schematically shown at 30) was used.

15kg of oil-pressed desolventized rapeseed flakes were mixed with 90kg of 60 ℃ water (6 parts water: 1 part starting flake) to form a slurry, and mixed for 10 minutes or more until mixed uniformly. The slurry, which was very viscous, was then fed to an impeller-driven auger-type filter fitted with a 6 inch diameter conical filter screen having 118 micron sized perforations (model FF-6 filter screen from vincent corporation, Tampa, florida, usa). The impeller pushes the slurry on the inner surface of the screen causing separation, thereby producing a concentrated filtrate containing small particles of cells and a filtered cake. The weight and dry matter content of the filtrate and the filter cake were then determined.

The filter cake obtained from the impeller filtration operation contains a considerable amount of water and is therefore less suitable for drying. However, during the first filtration step, the majority of the viscous liquid has been removed and the filter cake is directly treated with a belt filter press as described in the control example above. The filtration rate, the weight of the filtrate and the filter cake and the dry matter content were then measured as described above.

The cake discharged with the filter press was then re-slurried with 60kg of 60 ℃ water such that the total amount of water used for the two filtrations was equal to 10 parts water to 1 part dry canola flake powder. The second slurry was filtered using an impeller filter and the filter cake was then treated using a belt filter press as described for the first treatment. The process rate and measurements of the filtrate and press cake were as described for the first filtration. The processing rates of the belt press, the weights and dry matter contents of the filtrate and cake, the extraction efficiency and the dry matter loss of the comparative example (example 1) and the inventive example (example 2) are shown below.

The following abbreviations are used in the tables:

BP-belt press. BP-1 represents the first pass through the belt press in the example, while BP-2 represents the second pass through the belt press.

IF-impeller filter. IF-1 represents a first pass through the impeller filter in example 2 and IF-2 represents a second pass through the impeller filter in example 2. In example 1, no impeller filter was used.

Extract-a mixed liquid, indicated as 102 and 104 in fig. 1, in which the liquid includes, possibly, cell meat 102.

dm-dry matter.

ss suspended particulate matter.

Both impeller filters and belt filter presses can pass large quantities of valuable cell meat material in the form of small particles of suspended solids. Very little skin material was visibly incorporated into the filtrate.

In example 1, the high moisture slurry was easily extruded from both sides of the belt, resulting in a slow processing speed. In example 2, initially processing the slurry with an impeller filter, 69.2 kg of filtrate was removed and 21.8 kg of cake was produced, which was then easily processed by a belt press. The belt press had a processing speed 7.4 times greater than that obtained without the impeller filter to remove a large amount of liquid. The resulting biscuit dry content was 37%. The same results were obtained when treating the suspended cake by reforming the suspended cake with the first filtered cake. First, removal of large amounts of viscous liquid with an impeller filter can increase the processing speed of the belt press by a factor of 15, achieving a slightly better extraction efficiency. And about 75% of the protein in the rapeseed flakes can be recovered in the filtrate.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that other embodiments may be made. The specific embodiments are, therefore, not to be taken as limiting the invention, but rather the full scope of the invention is defined by the appended claims.

Claims (23)

1. A method for separating protein and/or carbohydrate components from insoluble fiber-containing components of a plant product, the method comprising the steps of:

a) mixing said plant product with water to form a slurry;

b) filtering the slurry with an impeller filter wherein the sweep action of the impeller is used to scrape the residue from the surface of the filter media thereby removing it from the area being filtered to yield a major liquid filtrate and a moisture-laden solid residue;

c) the water in the residue was removed by a pressure filtration apparatus.

2. The method of claim 1 wherein said impeller filtering step comprises continuously filtering the slurry with a driven auger that passes through a tubular filter.

3. The method of claim 1, wherein the impeller filtering step comprises periodically filtering the slurry mixed in the vessel with a driven impeller, a portion of the vessel being a filter medium, the impeller sweeping the slurry across the filter medium to discharge filtrate from the vessel.

4. A method according to any one of claims 1 to 3, wherein the step of pressure filtration comprises continuous filtration by passing the solid residue between two opposed filter belts which progressively pressurize the solid residue as it passes between the belts.

5. The method of any one of claims 1 to 3, wherein the pressure filtration step comprises continuous filtration by passing the solid residue through a screw press.

6. A method according to any one of claims 1-3, wherein said pressure filtration step comprises filtering the solid residue in a pressure filtration device comprising a pressure chamber having a filter medium forming a part of the boundary of the chamber by placing the solid residue in the pressure chamber and pressing said solid residue against said part of the boundary.

7. A method according to any one of claims 1-3, characterized in that in the method the main filtrate also comprises small solid particles rich in proteins and/or carbohydrates.

8. A method according to any one of claims 1 to 3, wherein the plant product is defatted oilseed fines.

9. The method of any one of claims 1 to 3, wherein the plant product is oil-pressed rapeseed flakes.

10. A process according to any one of claims 1 to 3, wherein the vegetable product is de-oiled rapeseed flakes obtained from a solvent-based oil extraction process.

11. A method as claimed in claim 10, in which method the main liquid filtrate contains particles of cell meat.

12. A separation apparatus for treating a solid product having a water soluble component, the apparatus comprising, in combination:

a) means for mixing the product with water to form a slurry;

b) an impeller filter in which residue is scraped from the surface of the filter medium by the sweeping action of the impeller to remove it from the area being filtered to separate the slurry into a filtrate and an aqueous retentate;

c) a pressure filtration device for further removing water from the aqueous retentate.

13. The apparatus of claim 12 wherein said impeller filter comprises a tubular filter medium having an auger impeller mounted therein, said impeller being in close proximity to said filter medium.

14. The apparatus of claim 12, wherein the impeller filter comprises a vessel including a filter media forming a portion of a boundary of the vessel and an impeller configured to move within the vessel against the portion of the boundary of the vessel.

15. Apparatus according to claim 13 or 14, wherein said filter medium is a mesh.

16. An apparatus as claimed in any one of claims 13 to 14 wherein the filter medium has perforations therein through which fine particulate matter including at least one of protein and carbohydrate can pass.

17. The apparatus of any of claims 13-14, wherein said filter media has a minimum aperture of 75 microns.

18. The apparatus of any of claims 13-14, wherein said filter media has a minimum pore size of 250 microns.

19. The apparatus of any of claims 13-14, wherein said filter media has 2500 micron maximum openings.

20. The apparatus of any of claims 13-14, wherein said filter media has a maximum opening of 250 microns.

21. An apparatus according to any one of claims 12 to 14, wherein said pressure filtration means comprises at least one pair of filter belts oriented so as to convey said solid residue while progressively pressurizing the solid residue between said pair of filter belts in the direction of movement of the solid residue.

22. Apparatus according to any of claims 12 to 14, wherein the pressure filtration means comprises a screw press.

23. Apparatus according to any of claims 12-14, characterized in that the pressure filter means comprise a pressure chamber, a part of which is bounded by the filter medium, and a piston which is adapted to be accommodated in the pressure chamber so as to press the solid residue located in the pressure chamber against the filter medium.